1. Field of the Invention
This invention relates to the permanent termination of fluid flow in pipelines by sealing the pipeline internally, and more particularly to an adhesive coated heat-recoverable pipeline internal termination plug which is inserted and subsequently heated to effect a return to or towards its original greater-diameter configuration, thereby exerting pressure against the pipeline walls, and contacting the adhesive coating thereagainst to affect a permanent seal.
2. Description of Prior Art
Inactive utility pipeline services develop no revenue for the supplier yet permanent abandonment to meet federal, state and local standards tranditionally necessitates a costly street excavation which is pure cost to the supplier and which presents a traffic nuisance to the public. Inactive pipelines in general present a wasteful leak potential and in the case of utility gas pipelines, a potentially explosive leak hazard, which is compounded by the problem of accelerated electrochemical corrosive deterioration at the capped ends of stub services. Urban renewal and changeovers to alternate fuels and power sources as a fallout of the current energy crisis have focused attention on the need for a method to permanently abandon inactive pipelines at reasonable cost.
An internally-placed seal or plug inserted at the heat of the service such as in a building basement or through a curb valve or through a low cost opening inside the curb would result in most significant cost savings by eliminating the need for the substantially more costly and more time consuming street excavation, subsequent closure and repaving. To that end, a method of filling the fittings at the main with a plug of epoxy material is described in "Low Cost Method For Abandoning Inactive Service", Peter J. Kassak, Corrosion Control Handbook, 4th Ed., Energy Communications, Inc., Pub., pps. 215-217, (1975). A collapsed umbrella of copper leaves is positioned inside the main and pulled back and secured against the service tap. Viscous epoxy plugging compound is mixed and loaded into a cartridge which is pushed down the service pipeline. The material is pushed out of the cartridge to fill the umbrella and to pack material against the inside of the main at the tap.
The effective sealing lifetime of the epoxy plug is questionable. Thermal expansion mismatch between the pipe material and the epoxy can result in destruction of sealing integrity over the years, a distinct disadvantage, especially in climates characterized by ground frost conditions and where water seepage into corroded service lines substantially stresses pipeline materials when the water freezes.
Sealing integrity is further disadvantaged by the geometries of the umbrella backstop with its copper leaves and the packing material with its irregular array, which are positioned in the main itself and extend into the fittings. Routine pipeline maintenance cleaning called "pigging" is commonly accomplished by dragging a cleaning brush or ball through the main. Any obstruction in the main can snag the pigging tool while predictably, dislodging the snag stresses the integrity of the obstruction, i.e. the subject sealing plug. Main obstruction is inherent in this system. Even backstopping alternates, such as the inflatable/deflatable balloon described in U.S. Pat. No. 3,607,361, "Balloon Backing for Pipe Lining", do not resolve the disadvantage completely. Some degree of obstruction is still present and debris is introduced into the main.
The on-site need to mix chemicals is a further complicating disadvantage of this prior art system. Moreover, the limited workable lifetime after mixing of a curable epoxy system requires a more highly skilled insertion crew and thus is an additional logistical disadvantage. The crew might break for lunch, for example, and subsequent insertion of the epoxy might be accomplished when the curing material is past the point of optimum bond formation with the pipe material since once a certain stage of cure has been reached, epoxy containing materials are not intrinsically adhesive.
These disadvantages have stimulated a continuing search for a suitable internally-placed pipeline sealing system. One alternate solution is described in "Research Vital to Polytechnic", Polytechnic Cable, Polytechnic Institute of New York, Pub., pps. 1 and 2, (Nov. 1979). This publication describes a plug utilizing an actuating rod made of titanium-nickel memory alloy. Memory alloys are alloy materials which remember a preprogrammed shape imparted to them at a temperature slightly above ambient because of a crystallographic phase transformation. The shape can then be altered at room temperature and stored at room temperature (or lower) for an indefinite time. Return to the remembered shape is accomplished by heating the part to a characteristic transformation temperature.
The polytechnic actuating rod is centered in a metal cylinder of about 3 inches in length and 1.3 inches in diameter after the rod has been stretched to 0.25 inches longer than its original length. Two neoprene rubber plugs are attached, one on each end. After insertion into the pipeline, heat is applied via electric current. The shrinking memory alloy exerts force on the rubber plugs which expand and bulge on each side forming a seal.
These blind plugs are apparently commercially inadequate and are not being marketed. The effective sealing lifetime of such a plug is questionable due to the deterioration characteristic of neoprene rubbers over time, such as oxidative embrittlement. The integrity of this seal results solely for the two rubber plugs and is a function of their elasticity which common knowledge and experience teaches is limited due to deterioration in service.
Moreover, the memory alloy relaxes on cooling below its transformation temperature and ceases to attempt to return further towards its undeformed shape. Thus, the rubber plugs are not continuously further biased once the rod is cooled, hence the nomer, "actuating" rod. The rubber will tend to attempt to return to a more relaxed configuration with time, such as by creep or cold flow, adversely affecting the permanence of the seal. Under the stress of pipeline pressures, typically 1/4 or 1/2 psi from the main side, the plug could leak, "walk" or even blowout. Neoprene rubbers are, of course, not intrinsically adhesive.